FIV is a slow-developing virus that causes immune dysfunction, just like the HIV virus in humans.

Most commonly clinical signs include recurrent bacterial and viral infections, due to weakening of the immune system.

Diagnosis is confirmed with blood tests.

There is no treatment for this disease; therefore prevention is very important.

What is Feline Immunodeficiency Virus?

• FIV is a lentivirus (slow virus), so named because of the slow development of disease. FIV is of the same family of viruses as human immunodeficiency virus (HIV), which causes acquired immunodeficiency syndrome (AIDS). It is important to remember that FIV is infectious only to cats.
  
• Immunodeficiency related to FIV infection occurs most often in free-roaming, male cats older than 6 years. Transmission of FIV is usually through cat bites incurred when fighting. Defense of territory explains the higher incidence of disease in male cats. FIV is occasionally transmitted to kittens by their mothers.
• Random testing of cats seen by veterinarians shows a healthy cat prevalence of 1% to 2% in the United States and up to 12% in Japan, where most cats are kept outside and are not neutered. Once cats develop FIV infection, they are infected for life.

Clinical Signs

• Cats with FIV, like people with HIV, have an acute phase of illness that begins 4 to 6 weeks after a bite from an infected cat. Fever, depression, and enlarged lymph nodes are usually seen in affected cats; these signs may last from weeks to months, and are usually mild enough that owners rarely notice. After recovery from the acute phase, cats may appear completely normal for 3 years or more. During this asymptomatic period, the FIV virus is gradually destroying the immune system, limiting the ability to fight infection.
  
• When the immune dysfunction is relatively mild, cats show signs associated with bacterial and viral infections such as mouth infections, abscesses, chronic nasal and eye discharges, skin infections, and diarrhea. These infections respond to the usual treatment, but not as well as expected, and often recur after treatment is completed.
  
• FIV can also affect the bone marrow, causing anemia. Parasitic diseases such as toxoplasmosis that normally cause only mild signs become life threatening. The FIV has an affinity for brain tissue and can produce personality changes. Shy cats may become aggressive and outgoing cats may hide. Malignancy of lymph node cells (lymphoma) may develop. Cats infected with FIV are also at higher risks of developing kidney failure.

Diagnosis

• When FIV is suspected, a blood test can be done. A negative test usually excludes a diagnosis of FIV, but an early infection (first 2 months) could be missed. A positive test with appropriate signs is quite reliable, but an occasional false-positive test can occur. A Western blot test (a more specific and definitive test) of blood confirms the diagnosis.

Treatment

• The response to treatment of FIV-infected cats depends on the degree of immune dysfunction.
• Unfortunately, no good antiviral drugs exist for the cat. Azidothymidine (AZT), a drug used in people to inhibit virus reproduction, works against the FIV virus but has significant toxicity in the cat. Other promising drugs are in development but they are not yet available. Most of the illness in FIV-infected cats results from secondary bacterial infections that can be controlled with antibiotics. Antibiotics can prolong the cat's life in spite of a poorly functioning immune system.

Prognosis

• A positive test for FIV is not a reason for euthanasia. A study of newly diagnosed FIV-infected cats showed that 7 of 11 cats were still alive 2 years later. We rarely know when cats become infected. A cat with early infection may have 3 or 4 more years of disease-free life.

Prevention

• Prevention with vaccination would be helpful but, as in people, an effective vaccine has not yet
  been developed.
• FIV-positive cats should be kept indoors for the safety of other cats (limit transmission by bite wounds) and to limit their exposure to diseases that they will not be able to fight.

Reference

• Ettinger SJ, Feldman EC: In Textbook of Veterinary Internal Medicine: 5th ed. Philadelphia: WB Saunders Co, 2000.